As the festival runs its course, a total of nine days ending Sunday, people won't necessarily want to get clean right away. Many will gladly walk the streets looking messy, and carefree.

"We got mud over us. Then we went into the sea," said Choi Jung-yoon, a 28-year-old office worker.

The free festival was started almost by accident in 1998 in this beach city about 90 miles southwest of Seoul. Several local businesses had developed a mud-based cosmetic product that wasn't selling.

Then somebody came up with a promotional gambit: Throw a little mud and the customers will come, they guessed.

According to Boryeong officials, more than 2 million people were expected to attend the festival this year. The local beach area has been a popular summer vacation destination for some time.

At the festival, strangers exchange high fives and bump fists. They hug, wrestle and pelt one another, sometimes becoming matching shades of gray.

The "Mud Experience World" portion of the festival includes a mud prison where inmates allow themselves to be deluged with mud by pretend guards. People run races on a splashy mud field. Nearby, celebrants gulp beer on the street, often while intoxicated and mud-faced.

In this conservative nation, South Korean festival-goers generally don't disrobe to get dirty. They leave that to foreigners, who seem more willing to strip down before diving into various games.

Shin Joon-hee, mayor of Boryeong, tells people not to be shy about revealing a little skin. "Once you come to Boryeong, you will become a beauty," he says.

And no worries about getting the mud off, organizers say. The sticky substance is saturated with minerals and, they say, provides skin-care benefits such as detoxification and moisturizing.

Organizers this year did have to cope with a problem before the event's kickoff when nearly 200 elementary school pupils suffered skin rashes after playing in mud planned for use in a section of the festival. Officials said the rashes apparently were caused by polluted water from a river near where the children had played, not by the mud.

"It did not happen in the main location of the festival," said Oh Moo-hyeon, an official with Boryeong's tourism department. "We are strengthening our safety management."

Overall, the event appeared to be going well during one recent day, as merchants spoke of brisk business and participants talked about having a lot of fun despite long lines and some rain.

"The thing I don't like is waiting in line for an hour to ride the mud slide," said Cokey Lin, 25, a Taiwanese graduate student. "And the weather as well."